Process for controlling wax deposition



PROCESS FOR CONTRQLLING .WAX DEPOSITION Morris Bock and James 6.Spalding, In, Dallas, Tex., assiguors to Sun Oil Company, Philadelphia,Pa., a corporation of New Jersey No Drawing. Application July 29, 1954Serial No. 446,680 r 15 Claims. (Cl. 252--8.S)

This invention relates to the production and transportation of crudepetroleum containing waxy constituentr More particularly, it is directedto controlling atent O the deposition of wax in conduits, such as welltubing wax during the course of their production. As the crude oil flowsfrom the producing formation to the surface,

a decrease in temperature occurs whereby waxy constituents may be causedto precipitate from the oil and to accumulate on the surface of thetubing and also on the sucker rods in pumping wells. When this occurs,accumulation of. wax in the tubing progressively decreases the rate ofoil production and thus requires that the tubing be cleanedperiodically. The frequency with which the cleaning has to be donevaries considerably depending upon the character of the crude oil andthe prevailing well conditions. .Usual times of pumping or flowing suchwells before cleaning becomes necessary range from a few days to severalmonths.

There are certain types of wells where the conditions are such that waxdeposition does not occur while the crude petroleum is in the Welltubing, although it does occur later. These are generally high pressuregas distillate wells. Upon removal from the well, thehydrocarbons areallowed to expand by reducing the pressure in order to cause coolingwhich will aid in effecting hydrocarbon condensation. The expandedhydrocarbons are then introduced to a separator to separate the liquidand gas phases from each other. In cases of this kind, it is not unusualfor wax deposition to occur in the separator and flow lines so thatcleaning of such equipment is eventually required.

The cleaning of wax deposits from Wells, flow lines, separators and thelike entails considerable expense which raises the overall cost ofoperating the Wells to maintain the desired rate of production. Knownmethods of cleaning include the use of mechanical scrapers, theemployment of solvents adapted to dissolve the wax and/or the use ofheat. The most usual practice with pumping Wells involves pulling thesucker rods from the well and scraping them each time that removal ofthe accumulated wax is required, which procedure necessitates theexpenditure of considerable labor. where the well is one which isincapable, even before substantial accumulation of wax has occurred, ofpro- In cases ducing at a rate in excess of its monthly allowableproduction rate, the decreased production resulting from the progressivedeposition of wax and from the necessity of shutting down to clean outthe deposits may represent a considerable loss to the producer.

The present invention provides a method for coneach of these otherforms.

ice

high molecular weight organic carboxylic acid. It has now been foundthat compounds of this class, when introduced periodically orcontinuously into the flow system, are particularly effective ininhibiting deposition of the wax and preventing or retarding itsaccumulation upon the surfaces of the well tubing, flow lines,separators and the like.

Compounds of the foregoing class are available commercially and have hadwideuse for various other pur poses in industry. They are prepared byconverting a hexitol, such as sorbitol or inannitol, into its cyclicether form by removal of water from the molecule and partiallyesterifying the ether with a high molecular weight.

organic carboxylic acid, and thereafter reacting the prodnot withethylene oxide to produce the polyoxyethylene derivative.

ide); hence the esterified product includes derivatives of Sorbitol andmannitol are preferred starting materials for preparing the waxinhibitor compounds of the invention, but any of the other hexitols,including dulcitol, iditol talitoland allodulcitol, 7

may be used if desired.

The organic carboxylic acid used for esterifying the hexitan shouldcontain 12-22 carbon atoms per molecule and can be a fatty acid,naphthenic acid, resin acid or acids which can be employed are lauric,myristic, palmitoleic, palmitic, stearic, oleic, ricinoleic, linoleic,linolenic, arachidic, erucic, resin acids, hydrogenated resin acids,

dehydrogenated resin acids, petroleum naphthenic acids and the like.

The amount of ethylene oxide reacted with the partial esters to producecompounds for use in accordance with the invention should be such thatthe number of oxyethylene groups is in the range of 4-30 per acidradical. Thus, the total number of oxyethylene groups is, from 4 to 30for the mono-esters, from 8 to 60 for the di-esters and from 12 to forthe tri-esters. More preferably, the total number of oxyethylene groupsper molecule for each of the three types of esters should be from 15 to25.

The following are specific examples of compounds for use in practicingthe invention: 15 polyoxyethylene sori bitan monolaurate, 2Qpolyoxyethylene sorbitan monopalmitate, 20 polyoxyethylenesorbitanmonostearate, 3t) polyoxyethylene sorbitan monooleate, 25polyoxyethylene sorbitan monoabietate, 20 polyoxyethylene sorbitanmononaphth'enate, di-esters and tri-esters corresponding'to theforegoing compounds, 20 polyoxyethylene sorbitan tri-tall oil esters,mannitol derivatives corresponding to the foregoing, etc. In the namesof the compounds set forth pounds of the class as specified herein, areeffective to prevent or retard the deposition ofwax from crude oils Theether formed from the hexitol is predominantly the mono-ether (hexitan)although it generally contains a minor proportion of the di-ether (hex,water, along with the oil.

invention to this well, its sucker rods had to be pulled or th'el'ike tofacilitate handling. Suitable mixtures for use.at the Well site can bemade by mixingapproximately.

equal parts of the active inhibitor compound and, the organic diluent.

In practicing the invention the wax inhibitor compound may be introducedeither periodically or continuously in-smallj amount into the crudepetroleum at the base of the well; As a matter of convenience, this maybe done simply by dumpinga suitable amount of the material once. a dayinto the annulus between the casing and tubing. The material sointroduced will migrate to the bottom of the well and find its way intothe well tubing along with crude oil from the formation. Whentreatmentof a Well is first begun, it is desirable to introduce from oneto. five gallons of the specified active compound,'admixed; with anequal volume of diluent, into the annulus and circulate the fluidsthrough the tubing and back to. the annulus for several hours, e. g. 412hours, before the well is allowed to produce. This procedure may berepeated for two or three days. Thereafter, the inhibitor compound maybe added once a day to the annulus inrelatively small amount. The mosteconomic dosage will vary some- What from well to' well but generallywill be inthe neighborhood of one pint of the active ingredient(excluding diluent) for each 15-50 bbls. of oil.

in retarding deposition of Wax tends to improve as the amount of theinhibitor added to the well is increased. Selection of the proper dosagefor any particular well canbe made by comparison of the costs ofoperating with and without the inhibitor being added.

It is presently uncertain why the use of compounds in accordance withthe invention effectively inhibits the deposition of wax upon thesurfaces of the Well tubing, flow lines or other equipment in'the flowsystem. However, it

is thought that the inhibitor compound forms a thin film on the surfaceofthe tubing and thereby reduces the tendency of the wax to adhere tothe metal. In some cases practice of the invention prevents anysubstantial accumulation of Wax in the tubing throughout a long periodof operation. In other cases the deposition is not entirely preventedalthough it is substantially retarded. Further- The effectiveness more,when deposition does occur while employing an inhibitor compound asabove specified, the deposited wax tends to be relatively soft ascompared to ordinary rod wax and is considerably easier to scrape fromthe tubing and sucker rods; hence the time and labor required for thescraping job are substantially reduced.

An illustration of the. invention as applied in actual field practiceinvolves a pumping well which was producing crude oil having an A. P. I.gravity of 40, a gasoline content (410 F. end point) of 36% by volumeanda wax content of 4% by weight. The maximum oil production rate thatcould be obtained for this well, was.

35 bbls. per day, and the well produced only traces of Prior toapplication of the and scraped. at 45 day intervals in order to maintainproduction. This cleaning operation usually yielded about 135 gallonsofhard rod wax each time the sucker rods were scraped. V

The foregoing well was then subjected to treatment according to theinvention by introducing daily into the annulus, about onequart of amixture containing 40 -50,%. of inhibitor compound in admixture, withdiluent; The

- inhibitor compound employed was 20 polyoxyethylene. sorbitan tri-talloil ester and itwas used inadmixture with kerosene during. a portion ofthe trialperiod andwith isopropanolduring another portion. After atrialperiod of about, 1'66 days, the sucker; rods Werelpulled. and

scraped. In this case only about 25 gallons of Wax were obtained; withthe wax being relatively soft in contrast-- to the hard producttheretofore deposited on the rods.

During another trial'period lasting for about days, this same well wastreated with 20 polyoxyethylene sorbitan trioleate in admixture, withkerosene in equal volumes. For the first two days, about 2 gallons/ dayof this mixture'was introduced into the annulus and circulated:

through the tubing for a while. Thereafter one quartz/- day of themixture was dumped into the annulus through a lubricator, and treatmentin this fashion throughout the test period was continued except for atime of 15 days during which no treatment was done. At the end of the125 day period, the sucker rodswere pulled from the well and scraped.This again yielded only about 25 gallons of relatively softwax. 7

Another pumping well located in the same field as the foregoing well hada normal production rate, priorto deposition of wax within the tubing,of 76 bbls./day of oil and -14 bbls./day of water, and it was necessaryto cleanythe; well at 30 day, intervals in order to maintain the desiredproduction. Normally about 225 gallons of hard rodwax was obtainedduring each cleaning. Treat ment' of this well was then begun, utilizing21:50:50 rn'mtureof kerosene and 20 polyoxyethylene sorbitan tri-talloil'- ester.- the mixture Was introduced into the annulus andcirculatedthrough the tubing for a time; and thereafter the inhibitormixture was dumped into the annulus in amount of 3" quarts/day. After 43days of operation, the rods were pulled for inspection and about 25gallons of wax were.

removed by scraping. The well was then'placed back'inoperation and the 3quarts/ day treatment was continued.

15 gallons of wax. the waxrecovered was soft and could readily bescraped from the sucker rods.

The examples described above illustrate the invention .as applied to theinhibition of Wax deposition Within,

the well tubing. In cases where the wax does not deposit in the welltubing due to the prevailing well conditions.

. but does subsequently deposit in flow lines, separatorsorotherequipment, the inhibitor does not need to be addedto the .well itself asdescribed above, but instead may be introduced into the crude oil at asuitable point be-' In any event it should be noted that the. inhibitormaterial should be applied, whether it yond the well head.

be .withinthe well or in flow lines or other equipment, prior to anysubstantial accumulation of wax therein;

In other words the polyoxyethylene hexitan partial esters employed\according to the present invention do not.

function as solvents for wax already accumulated on surfaces andareineffective in removing wax previously deposited; Hence the treatmentcarried out with these materials should'be proceded by a cleaningv ofthe [system to remove any wax already accumulated. This 'perrnits theinhibitor to come in contact with the metal surfaces andevidently formthereon a film which prevents hard wax from clinging to the metal.

We claim:

groups per acid radical.

2. Process according to During the first three days 2 gallons/day ofclaim l wherein s aid"poly-" oxyethylene ether is an ether of sorbitantri-tall oil ester and contains 15-25 oxyethylene groups per molecule.

5. Process according to claim 1 wherein said polyoxyethylene ether is anether of sorbitan tri-fatty acid ester and contains 15-25 oxyethylenegroups per molecule.

6. Process for inhibiting the accumulation of wax from crude petroleumin the tubing of a producing well which comprises introducing into theWell periodically at least once a day an inhibiting amount of apolyoxyethylene ether of a hexitan partial ester of an organiccarboxylic acid having 12-22 carbon atoms and selected from the groupconsisting of fatty, naphthenic and resin acids, said ether containing4-30 oxyethylene groups per acid radical.

7. Process according to claim 6 wherein the amount of thepolyoxyethylene ether introduced is" about one pint for each 15-50 bbls.of oil produced from the well.

8. Process according to claim 7 wherein said polyoxyethylene ether is anether of a sorbitan ester containing15-25 oxyethylene groups permolecule.

9. Process according to claim 8 wherein said sorbitan ester is atri-ester.

10. Process for inhibiting the accumulation of wax from crude petroleumin the tubing of a producing well which comprises continuouslyintroducing into the well an inhibiting amount of a polyoxyethyleneether of a hexitan partial ester of an organic carboxylic acid having12-22 carbon atoms and selected from the group consisting of fatty,naphthenic and resin acids, said ether containing 4-30 oxyethylenegroups per acid radical.

11. Process according to claim 10 wherein the amount of thepolyoxyethylene ether introduced is about one pint for each 15-50 bbls.of oil produced from the well.

12. Process according to claim 11 wherein said polyoxyethylene ether isan ether of a sorbitan ester containing 15-25 oxyethylene groups permolecule.

13. Process according to claim 12 wherein said sorbitan ester is atri-ester.

14. In the transportation of crude petroleum from a well through a flowsystem wherein wax in the petroleum normally tends to accumulate uponthe surfaces of equipment, the method of retarding such accumulationwhich comprises introducing into the petroleum, prior to substantialaccumulation of wax upon such surfaces, an inhibiting amount of apolyoxyethylene ether of a hexitan partial ester of an organiccarboxylic acid having 12-22 carbon atoms and selected from the groupconsisting of fatty, naphthenic and resin acids, said ether containing4-30 oxyethylene groups per acid radical.

15. Method according to claim 14 wherein said polyoxyethylene ether isan ether of a sorbitan tri-ester containing 15-25 oxyethylene groups permolecule.

References Cited in the file of this patent UNITED STATES PATENTS1,892,205 De Groote Dec. 27, 1932 2,533,878 Clark et a1 Dec. 12, 19502,753,303 Barker July 3, 1956 OTHER REFERENCES Spans and Tweens-pamphletpub. 1945 by Atlas Powder Co. of Wilmington, Delaware, page 17.

1. PROCESS FOR INHIBITING THE ACCUMULATION OF WAX FROM CRUDE PETROLEUMUPON SURFACES OF A SYSTEM THROUGH WHICH THE CRUDE PETROLEUM ISTRANSPORTED WHICH COMPRISES INTRODUCING INTO THE SYSTEM, IN THE PRESENCEOF THE CRUDE PETROLEUM AND PRIOR TO THE ACCUMULATION OF SUBSTANTIALAMOUNTS OF WAX THEREIN, AN INHIBITING AMOUNT OF AN INHIBITOR THEESSENTIAL ACTIVE INGREDIENT OF WHICH IS A POLYOXYETHYLENE ETHER OF AHEXITAN PARTIAL ESTER OF AN ORGANIC CARBOXYLIC ACID HAVING 12-22 CARBONATOMS AND SELECTED FROM THE GROUP CONSISTING OF FATTY, NAPHTHENIC ANDRESIN ACIDS, SAID ETHER CONTAINING 4-30 OXYETHYLENE GROUPS PER ACIDRADICAL.